FSA chief executive Catherine Brown told the BBC: "We are demanding that food businesses conduct authenticity tests on all beef products, such as beefburgers, meatballs and lasagne, and provide the results to the FSA."

The FSA's website advises consumers: "There is no reason to suspect that there's any health issue with frozen food in general, and we wouldn't advise people to stop eating it."

Peter Kendall, president of the National Farmers' Union, said farmers who had suffered from food scares in the past were "furious" over the horsemeat revelations because they had already "raised their game".

He urged consumers to buy British meat to be sure of what they are eating.

Findus is the latest company to be caught up in the controversy surrounding contamination of meat products, which has affected firms in the UK, Irish Republic, Poland and France.

Last month, Irish food inspectors announced they had found horsemeat in some burgers stocked by a number of UK supermarket chains, including Tesco, Iceland and Lidl.

Ms Creagh expressed fears there were further revelations to come from the food industry.

"What we have had over the last four weeks is a constant drip, drip, drip of revelations from the food industry, from the Food Standards Agency, and what I am worried about is that the more they are testing for horse, the more they are finding," Ms Creagh said.

She suggested further guidance was needed on whether people should eat other processed foods labelled as containing beef.

Mr Heath said the FSA was undertaking the "biggest testing of beef products that has ever taken place" in order to offer reassurance.

Prime Minister David Cameron, speaking in Brussels, described the latest revelations as "very shocking" and "completely unacceptable".

A statement from the British Meat Processors Association (BMPA) said it "deplores the latest reported incidents of gross contamination of some processed meat products".

It urged members to review their raw material and ingredients-sourcing procedures.

The supermarket chain Aldi was also advised to withdraw its Today's Special Frozen Beef Lasagne and Today's Special Frozen Spaghetti Bolognese by French supplier Comigel.

An Aldi spokesman said the meals had been withdrawn immediately and it was carrying out its own investigations.